Grounding device for rotary electrical printer and method

ABSTRACT

The printer records images in the form of dots on electrical discharge-sensitive paper which has a conductive coating on one surface. A plurality of styli are mounted on a rotor. The paper is fed continuously through a curved guide in a direction perpendicular to the plane of rotation of the rotor. This divisional patent is directed to the feature whereby current is supplied to the styli from a power supply through the conductive coating on the paper. The return path to the power supply is made by means of a simple brush consisting of a curved, helical spring. The spring makes good electrical contact and also serves to help shape the paper into an arc before it passes over the rotor.

This is a division of U.S. application Ser. No. 611,785, filed Sept. 9,1975, now U.S. Pat. No. 4,100,551.

This invention relates to image recording and printing, and particularlyto rotary printing. In its preferred embodiment, the invention isdisclosed in use in a rotary printer of the type in which images areformed by electrical discharges selectively positioned ondischarge-sensitive paper.

As the speed of modern data-processing equipment has increased, so hasthe need for a high-speed, low-cost data printer. Very high-speed dataprinters have been developed. However, such printers usually are verycomplex and expensive. Much cheaper printers have been devised, butusually such printers are slow, and also are complicated. As a result,the cost of such printers, in terms of dollars per unit of printingspeed (character per second), has been undesirably high. Furthermore,such prior printers have been unduly complicated and large. Themaintenance costs have been relatively high, and the loss of operatingtime due to malfunction also has been undesirably large. Also, manyprior printers are very noisy in operation.

In accordance with the foregoing, it is a major object of the presentinvention to provide a recorder or printer whose speed is relativelyhigh and whose cost is low; a printer whose cost per unit of speed isvery modest. Furthermore, it is an object to provide such a printerwhich is small, simple and reliable. Furthermore, it is an object toprovide such a device which is relatively smooth and quiet in operationso that it does not disturb people when printing.

In accordance with the present invention, the foregoing objects are metby the provision of a rotary electrically-operated printer having arotor and a plurality of electrically actuatable print members securedto the rotor. Drive means are provided for rotating the rotor to movethe print members across a record surface.

Means are provided for producing electrical position signals indicatingthe position of the rotor, and actuating means responsive to theposition signals are provided for selectively electrically actuatingeach of the print members when the rotor is in a pre-determinedposition.

In accordance with one feature of the invention, means are provided forchanging the position of the printing produced on the record surface byat least one of the print members, the changing means comprising meansfor changing the time separation between successive actuations of theprint members. By this means, the relative positions of the printedimages can be adjusted on the record member without movement of theprint members on the rotor. This avoids the necessity for re-balancingthe rotor and other adverse effects which might be caused by mechanicaladjustment of the print members.

Preferably, the record surface has the form of a strip of electricaldischarge-sensitive paper which is wrapped part-way around the rotorwhen making contact with the print members. It also is preferred thatthe paper strip be moved transversely across the rotor in a directionperpendicular to the plane of rotation of the rotor.

In accordance with another feature of the invention, characters areprinted by forming them from dots produced by a plurality of styliarranged in axially-extending groups. Each print member or head includesone such group of styli. Preferably, there are enough styli in each ofthe groups to form a complete character with one pass across therecording surface. Thus, one pass of the rotor over the recordingsurface will print at least as many characters as there are print heads.

It is preferred that the characters be formed into words which extendlongitudinally of the record strip, and that the strip be wide enough toaccommodate a number of lines of text matter to be printed. Codedinformation representing the characters is stored in an electricalmemory and then read out in a sequence such that each print head printscharacters in vertical columns, the characters in each column beinglocated in different lines of text matter. Thus, during each pass acrossthe record strip, each head will print not just one character, but asmany characters as there are lines of characters to be printed. In thepreferred device, there are three such heads so that for each revolutionof the rotor the number of characters which will be printed is equal tothree times the number of lines of text. As a result, rather highprinting speeds can be achieved with moderate rotor speeds.

It is also within the scope of the invention to print the words acrossthe strip rather than longitudinally. In this case, the printing speedalso will be relatively high.

In accordance with a further feature of the invention, the electricalposition signals for indicating the position of the rotor are producedby indicia which rotate with the rotor and which are spaced apart by thedesired spacing between dots in the printed images. Preferably, theindicia are opaque lines on a transparent disc mounted on the same shaftas the rotor.

A plurality of detectors is provided for detecting the indicia. It isdesired that the number of detectors equal the number of recordingheads. One of the detectors remains stationary, and the other two can beadjusted angularly around the disc to effectively alter the enabling anddisabling of each of the three stylus heads without actually moving anyof the heads. This permits adjustment of character alignment tocompensate for uneven stylus wear and similar problems, without anymechanical adjustment of the heads on the rotor.

The memory which is used to store the character codes desirably is oneinto which data can be recirculated so as to repeat the printed text tomake duplicate copies.

The paper strip preferably is fed continuously past the rotor at a speedwhich is directly proportional to the rotor speed. This ensures the samespacing between characters or lines (depending on which direction wordsare printed in) regardless of the rotor speed. This is accomplishedcompactly by gearing a paper feed roller to the same shaft as the onewhich drives the rotor.

The shaft is driven by a D.C. motor which has relatively high torque atlow speeds, is relatively inexpensive, and which can be operated bybatteries so as to make the printer portable.

The paper feed roller extends outwardly from a housing. A curved guidefits over the housing to guide the paper into a cylindrical sleeve whichis used as a platen which supports the recording paper, and upon whichthe styli ride when not contacting the paper. The paper feed rollermates with an idler roller mounted in the guide, and pulls paper from aroll.

Paper from the roll passes over a guide bar which is locatedapproximately in the plane of travel of the top of the arched paperthrough the printer. The guide bar is located so as to force the paperto bend through a substantial angle so that the point of delivery of thepaper to the printer will remain approximately the same despitevariations in the diameter of the paper roll. This prevents jamming andbunching of the paper.

Especially simple means are provided for electrically connecting theconductive portion of the paper to the return connection of the voltagesupply. This should be provided in order to ensure electrical dischargesbetween the styli and the paper. The simple grounding means comprises ahelical spring on a curved rod. The spring is electrically conductiveand is connected to ground. It is bowed into a shape so that it fitsneatly against the concave surface of the paper as it passes through theprinter. The spring also serves as a part of the guide structure whichshapes the paper strip into an arc.

Because the speed of the paper feed, the timing disc and the rotor allare equal or directly proportional to one another at all times, theprinter will operate accurately at a very wide range of speeds. In orderto ensure that the blackness and readability of the printing isrelatively uniform despite such speed variations, an automatic blacknesscontrol circuit is provided. The speed of the rotor is sensed, and thevoltage applied to the styli is varied directly with the speed so thathigher voltages are applied at higher speeds, and vice versa. Thispromotes relatively uniform blackness of the printed images.

The result of the foregoing features is a printer which meets theobjects set forth above. That is, the printer is notably small, simplein construction and lightweight. Nonetheless, it is fast, relativelyinexpensive and easy to maintain, and is quiet in operation.

The foregoing and other objects and advantages of the invention will beset forth in or apparent from the following description and drawings.

In the drawings:

FIG. 1 is a front perspective view of a printer constructed inaccordance with the present invention;

FIG. 2 is a rear perspective view of the printer shown in FIG. 1, withthe paper guide raised, and with some of the paper removed;

FIG. 3 shows a section of the paper recording strip used in the printerof FIG. 1 and bearing a reproduction of printing actually produced bythe printer;

FIG. 4 is an exploded front perspective view of the printer shown inFIG. 1;

FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 1;

FIG. 6 is an elevation view of the rotor of the device of FIG. 1 takenin the direction of line 6--6 of FIG. 5;

FIG. 7 is an elevation view of the timing disc of the device shown inFIGS. 1 through 5, and is partially schematic;

FIG. 8 is a set of waveform diagrams demonstrating the operation of thetiming disc and associated electronic circuitry;

FIGS. 9 and 10 comprise the electrical control circuit of the printershown in FIGS. 1 through 5;

FIGS. 11 and 12 are partially schematic elevation views of a componentof the printer, with the component being shown in two differentoperating positions in the two figures; and

FIG. 13 is a plan view, partially schematic, illustrating anotherembodiment of the invention.

GENERAL DESCRIPTION

FIGS. 1 and 2 show a preferred embodiment 20 of the printer constructedin accordance with the present invention. The printer 20 includes a baseplate 22, a cylindrical housing 24, a cylindrical sleeve 26 which isused as a platen, a rotor 28 mounted on a shaft 48 so as to rotate inthe sleeve 26, and a drive motor 30 for rotating the rotor 28. A timingdisc 54 (FIG. 2) for timing the printing also is mounted on the shaft48.

Electrical discharge-sensitive paper 36 is stored in a roll 34 containedin a dispenser 32. The paper 36 passes upwardly from the roll 34 over astraight guide bar 35 towards a curved paper guide 38. The guide 38 ishinged to the outer surface of the housing 24 at 40 so that it can beraised easily in the manner shown in FIG. 2. As it is shown in FIG. 1, alatch 42 holds the guide 38 down when the printer is in operation.

Referring to FIG. 2, a drive roller 56 is provided which pulls the paperfrom the roll 34, drawing it through the curved guide 38 so that thepaper forms an arc, and feeds the paper through the sleeve 26 near itsupper most inside surface. After the printing has been formed on theundersurface of the paper 36, the paper emerges from the left edge ofthe sleeve 26 as shown in FIG. 1. A paper tear ring 46 is provided atthe left edge of the sleeve 26. The ring 46 has a serrated upper edge 47to permit a length of the paper strip to be torn off easily.

The undersurface (that is, the concave surface) of the paper strip 36 iscoated first with a dark material, and then with a light-coloredmaterial such as aluminum or zinc oxide which can be eroded or vaporizedaway by an electrical discharge or spark. The rotor 28 has three stylusheads 62, 64 and 66 each with five parallel equidistant axially-spacedstyli 68 (see FIGS. 5 and 6).

As it will be explained in greater detail below, the paper feed roller56 and the rotor 28 are driven continuously by the drive motor 30. Thestyli are selectively energized so as to form images on the underside ofthe paper by the formation of dots in a five dot by seven dot matrix.

An example of printing produced by the printer 20 is shown in FIG. 3.Each stylus head has five wires, which is enough to produce all the dotsfor the horizontal portions of characters to be printed. Thus, each timeone of the stylus heads passes over the recording paper, it will produceat least one printed character.

It is preferred that the words be printed on the strip as shown in FIG.3; that is, in the longitudinal direction indicated by the arrow 31.Furthermore, when several lines of text are to be printed, the data isstored in a memory in the device and is read out so that each stylushead will print an entire vertical column of characters, one characterfrom each of the lines. For example, the first column A of characters inFIG. 3 was printed by a single pass of a single stylus head; the columnB was printed by a single pass of a second stylus head, and column C wasprinted by a single pass of a third stylus head. Since there are threestylus heads, three columns of characters are printed per revolution ofthe rotor. Thus, the number of characters per revolution which thedevice will print is equal to three times the number of lines beingprinted.

Of course, it also is possible to form words in a vertical directioninstead of in the horizontal direction shown in FIG. 3. The speedcapabilities of the printer when operating in such a mode are comparablewith those in the other mode.

The printer 20 now will be described in detail.

DRIVE SYSTEM

Now referring to FIGS. 4 and 5, the drive system of the printer 20includes the shaft 48 and the drive motor 30, both of which already havebeen described. The motor 30 is mounted on an end plate 70 for thehousing 24 by means of screws 80. To the output shaft 76 of the motor 30is secured a toothed drive wheel 78 which drives a toothed-timing belt50 (see FIGS. 2 and 4) to drive large toothed wheel 52 which is securedto the shaft 48. The sizes of the wheels 78 and 52 are such as toproduce a speed reduction of four to one. The timing disc 54 is securedto the wheel 52 and thus is secured to the shaft 48.

The shaft 48 is mounted in ball bearings 72 in the end plate 70, and aretainer 74 is secured to the right end of the shaft. (See FIG. 5).Another end plate 88 is provided at the opposite end of the housing 24.The shaft rotates in ball bearings 92 in the end plate 88, and isretained by a retainer 108 secured to the shaft.

The rotor 28 is mounted on a spacer 110 (see FIG. 4 as well as FIG. 5)by means of screws, and the spacer is similarly attached at its otherend to a slip-ring disc 104 which abuts against the retainer 108. Thespacer, slip-ring, and rotor 128 are held against the retainer 108 bymeans of a threaded nut 114 which screws onto threads 49 (FIG. 4) on theleft end of the shaft 48. Thus, the rotor 28, the spacer 110, theslip-ring disc 104, the gear wheel 52 and the timing disc 54 all rotatetogether at the same speed.

The rubber paper feed roller 56 is driven by gearing coupling it to theshaft 48. As it is shown in FIGS. 4 and 5, the roller 56 is rotatablymounted on a shaft 96 which is secured in an upper extension 89 (SeeFIG. 4) of the end plate 88. A slot 91 is provided through which theupper surface of the roller 56 extends.

A lower extension 90 of the end plate 88 forms the bearing support for ashaft 84 to which is secured a worm gear 86 which meshes with a worm 82secured to the shaft 48. This combination drives a bevel gear 92 whichmeshes with another bevel gear 94 on the shaft 96 which drives the paperfeed roller 56 at a speed substantially slower than that of the rotor28.

The feed roller 56 mates with an idler roller 98 which is mounted on ashaft 100 in the curved paper guide 38. A cover 102 fits over the idlerroller 100 to protect it.

As it can be seen in FIG. 5, the recording paper 36 is pinched tightlybetween the two rubber rollers 56 and 98 so that the rotation of theroller 56 will pull the paper through the printer substantially withoutany slippage.

PAPER GROUNDING MEANS

FIG. 10 shows schematically the electrical circuit formed when a sparkis formed between a stylus 68 and the paper 36. The conductiveunder-surface 39 of the preferred recording paper must be connected tothe return terminal of the voltage supply 69 which is connected to thestylus 68 in order to produce electrical discharges. Since that returnterminal is grounded, the undersurface of the paper must be grounded.

This is accomplished by a means of a unique grounding device which isshown in FIGS. 2, 4 and 5. The grounding device consists of a helicalconductive spring 58 which is wound around a curved metal rod 60 whichis secured to the end plate 70 in the manner shown in FIG. 4 and whichis connected to ground. The ends of the spring 58 are held in place bymeans of retaining rings 61.

As it is shown in FIG. 5, the rod 60 curves forwardly as well as into anarc so that it fits underneath the right edge of the cover 38. The upperportion of the coils of the spring resiliently press against theunderside of the paper 36 and force it upwardly against the guide 38.The many coils of the spring provide numerous relatively closely spacedcontacts to make good grounding contact with the undersurface of thepaper.

This combination ground connection and paper tensioning means alsoserves a third function; that of helping to shape the paper into an arcso that it will pass easily through the guide 38.

PAPER DISPENSING

As it is shown in FIGS. 1, 2, 4 and 5, the paper roll 34 is stored on aspindle 120 whose ends fit into slots 118 in a pair of end plates 122 ofthe dispenser 32. The plates 122 are secured to the base plate 22 of theprinter. The friction created by the various components of the dispensertends to prevent over-run of the paper feed roll after paper feeding hasstopped.

As it is most readily apparent in FIG. 5, the bar or roller 35 servesthe function of causing the paper coming from the roll 34 to be bentthrough a substantial angle before passing on towards the printer.However, the bar always delivers the paper at approximately the sameheight to the printer, which would not be the case if the paper werepulled directly from the roll 34. Substantial movement of the dispensingpoint is undesirable in that it tends to cause bunching or wrinkling ofthe paper and thus prevents smooth feeding of the paper. Therefore, thedispenser 32 dispenses the paper strip to the printer uniformly andsmoothly.

ROTOR CONSTRUCTION

FIG. 6 shows the construction of the rotor 28 and the positions of itsthree stylus heads 62, 64 and 66. FIG. 6 is a partially schematic viewof the rotor 28, taken in the direction of line 6--6 of FIG. 5, with thespacer 110 and other elements omitted.

As it can be seen in FIG. 6, the points of contact between the styli 68and the circle 125 which represents the internal surface of the platensleeve 26, are indicated by reference numerals 119, 121, and 123. Thestyli 68 are mounted in a solid epoxy resin base which is secured to abracket 128 which is mounted on the rotor 28. The bracket 128 has acurved slot 130 with a screw 132 to allow the stylus head to be movedoutwardly or inwardly to increase or decrease the pressure of the stylion the platen or the paper on the platen.

As it can be seen in FIG. 6, the angle between the styli and the radiuslines extending through the points 119, 121 and 123, is approximately70°. The angle formed between the styli 68 and the tangent line 127 atpoint 119 therefore is 20°. Thus, the styli travel over the platen andthe paper at an angle substantially less than perpendicular. This makesfor smoother operation of the mechanism and reduces the likelihood ofthe styli tearing the paper when the styli cross over from the platenonto the edge of the paper.

Referring again to FIG. 5, it can be seen that the platen sleeve 26 isof a diameter substantially larger than that of the housing 24. This isnecessary so that the paper 36 will enter the inside surface of theplaten sleeve. The lower two-thirds 116 of the rear edge of the sleeve26 is of a smaller diameter so that it will fit onto the flange 93 ofthe end plate 88 where it is fastened in place by means of three screws(not shown).

The paper tear ring 46 is fitted into a recess 95 in the inside surfaceof the front edge of sleeve 26.

As it also is apparent from FIG. 5, each of the stylus heads 62, 64 and66 is connected to terminals at the rear of the slip-ring board 104 bymeans of wires 112 (also see FIG. 9). The terminals connect through theboard 104 to the slip-rings on the other side of the board 104. It alsoshould be noted that the stylus heads 62 and 64 are shown in FIG. 5rotated from their actual positions so that they can be illustrated moreclearly.

DISCHARGE TIMING STRUCTURE

The timing of the formation of dots by the styli is important to theaccurate printing of characters and other images. Referring now to FIGS.2, 4, 5 and 7, this timing function is provided by means of thetransparent disc 54 which has a series of thin opaque black lines 166(FIG. 7) and a single wide black line 168 applied to the disc. Ideally,the three sensors A, B and C would be 120° apart from one another, asare the three stylus heads 62, 64 and 66. However, the construction ofthe housing 24 and the paper guide 38 does not permit this. Because ofsuch constructional restraints, sensors A and C are placed 180° apartfrom one another, and sensors A and B are placed 60° apart. Sensor B isfixed in position. However, sensors A and C are movablecircumferentially with respect to the disc 54 so as to adjust the timingof the start and stop of printing by the stylus heads relative to oneanother. This makes it relatively easy to make the initial headalignment, and also makes it possible to easily adjust for uneven wearof the styli and other causes of misalignment of the printing withoutmoving the stylus heads. This avoids unbalancing the rotor and makes theadjustment process quite simple.

TIMING ADJUSTMENT

Referring to FIGS. 4, 11 and 12, as well as FIG. 7, sensor B, the fixedsensor, includes a detector structure 146 fastened to a mounting plate148. The detector structure 146 includes a U-shaped housing, one arm ofwhich includes a small light-emitting diode (LED) 153 (FIG. 11) whichshines its light towards the other arm which contains a smallphoto-transistor 155 to detect the light. A mask (not shown) comprisinga small piece of film which is opaque except for a small thin slitcovers the photo-transistor so as to admit only that light which fallson the thin slit.

The detector 146 of sensor B is inserted through a hole 138 in thehousing 24 and is secured in place after the disc 54 has been mounted inthe housing. The two arms of detector 146 fit around the edge of thedisc so that the light from the LED shines through the disc in the areawhere the markings 166 and 168 are located and is detected by thephototransistor.

Each of the other sensors A and C also includes an identical detector146. The detector 146 in each sensor A and C is mounted on an L-shapedbracket 154 which is pivotably connected at 152 to a mounting bracket150. The bracket 154 has a long arm with a longitudinal groove 156.

Still referring to FIGS. 4, 11 and 12, two adjustment cam devices 158and 160 are provided. Each has a body which is fitted rotatably into ahole in the end plate 70 of the housing 24 and has a slotted head whichpermits the device to be turned with a screwdriver. Each device 158 and160 also has an eccentrically-mounted pin 162 or 164. As it is shown inFIGS. 11 and 12, the pin 162 or 164 fits into the groove 156. As thehead of the cam device 158 or 160 is rotated, the arm of the bracket 154is raised upwardly or lowered about the pivot point 152 so as to changethe location at which the detector senses the lines 166 and 168. Thepivot points 152 are shown schematically in FIG. 7.

The detailed operation of the disc 54 and the sensors A, B and C intiming the printing of the printer will be explained in detail inconnection with FIGS. 8 through 10. However, in general, each of thethin, closely-spaced lines 166 times the placement of one dot (or onerow of up to five dots), and the wide pulse mark 168 serves as areference mark. Very precise adjustments in the printing placements canbe made by use of the cams 158 and 160 to move slightly the location ofeither or both of the sensors A and C relative to the sensor B so as tochange the relative starting and stopping times for printing produced bythe stylus heads.

ELECTRICAL CONTROL CIRCUITRY

FIG. 9 shows the electrical control circuit for the printer 20. Thedrive motor 30 is shown in the lower left hand corner of FIG. 9, and thestyli 68 are shown in the upper right-hand corner of the drawing. Theslip-ring disc 104, the brushes 106 contacting the slip-rings and thewires 112 leading from the slip-rings to the styli also are shown in theupper right hand corner. It is evident from FIG. 9 that each of theslip-rings is continuous so that each of the brushes 106 continuously isin contact with three styli, one from each of the three stylus heads.

The position of each such stylus is the same in each of the heads. Thatis, the outermost brush is connected to the first stylus in each head;the next brush to the second stylus, and so forth. This means that thestyli in all three heads (labeled groups A, B and C in FIG. 9) areenergized simultaneously. Therefore, the paper strip 36 should notextend more than one-third of the circumference of the platen 26.Otherwise, extraneous printing will be done on the strip. Of course, ifthe use of a wider strip is desired, then the styli can be energizedselectively by means of segmented slip-rings.

D.C. is supplied throughout the control circuit by either a D.C. powersupply, if 117 volts 60 H_(z) power is the available source, or from abattery.

In the central upper portion of FIG. 9 is shown a memory 200 consistingof six 480 bit shift-registers. Connected to the output of memory 200 isan ROM code converter 202 commonly called a "character generator", whichconverts character identification signals from the memory 200 intocorresponding dot matrix signals appearing on five output lines 203. Thedot matrix signals are adapted to enable selected ones of the five styliwhich are in contact with the paper strip to be energized so as to formone row of dots in a particular character to be printed.

The code converter 202 is addressed by means of three input leads264,266 and 268 in order to produce on the output lines 203 successivelythe information to form seven successive rows of dots for a givencharacter, thus enabling the printing of the character in 5×7 dot matrixform. This procedure will be described in greater detail below.

DATA ENTRY

The memory 200 has a capacity sufficient to store characters for twelvelines of text, each line being forty characters long. By the addition ofmore shift registers, the storage capacity of the memory 200 can beincreased. With a paper strip width of four inches and charactersapproximately 3/16th inch high, and with minimum spacing between lines,up to twenty-four lines can be printed across the paper strip. The linescan be made about as long as one desires, if one is willing to add thenecessary storage capacity to the memory. In fact, if the characters areprinted in a single line, and if a "FIFO" memory is used instead of thememory 200, the line can have a virtually unlimited length.

Data is applied to the six input lines 204 to the memory 200. A memorycontrol circuit 206 is provided for reading and writing to and from thememory 200. A high-frequency clock signal (e.g. 1 MHz) is applied overinput line 226 to one input of a NAND gate 228. Strobe pulses areapplied, at a somewhat lower frequency, over another input line 216. Thestrobe pulses are delivered to one input of a gate 218. During dataentry, a D-type flip-flop 236 (lower left-hand corner of FIG. 9) is inthe reset condition in which a signal appears on output Q and noneappears on the output Q. The "low" signal on Q enables gate 218 whichdelivers strobe pulses through another gate 220 and an AND gate 222 overa read/write line 224 to the memory 200. The strobe pulses cause data tobe entered on the common data entry line 225 to the shift registers inthe memory.

When the flip-flop 236 is reset, the Q signal from flip-flop 236 isapplied over a line 224 to inhibit a gate 219 to prevent the reading ofdata through that gate.

Simultaneously with the read-in of data to the memory 200, the output ofgate 222 is delivered over line 230 to the clock input of another shiftregister 232 which also has a storage capacity of 480 bits and isidentical to the shift registers in the memory of 200. The shiftregister 232 is used as a detection device to detect when the memory 200is full, and to signal the start of the printing operation.

START MOTOR

When the shift register 232 is full, it sends out an output signal overline 234 to the clock input of the flip-flop 236. This "sets" theflip-flop and creates a signal on the Q output line which is sent overline 238 to a motor drive circuit 208, which is a semi-conductor relaywhich completes the circuit to the drive motor 30 and starts it running.

The change of flip-flop 236 to the "set" condition enables gate 219 andthus makes it possible to read data out of the memory during printing,as it will be described below. Also, gate 218 is disabled by the signalon Q, so that data no longer can be written into the memory from theinput lines 204.

SETTING THE END MARGIN ON THE RECORD STRIP

The operation of the flip-flop 236 also causes a change of state on itsQ lead, and this actuates a margin counter circuit. A counter 246 countstwo "column sync" signals representing two revolutions of the timingdisc 54 (not shown in FIG. 9) before it permits the printer to startprinting in order to provide a definite unprinted margin on the paperbetween the matter to be printed and the cut end of the paper strip.

COLUMN SYNC SIGNAL GENERATION

At the lower right-hand edge of FIG. 9 are shown the three sensors A, Band C shown in FIGS. 4 and 7 which detect the narrow timing marks 166and the wide timing mark 168 on the spinning disc 54. Included in thedetectors A, B and C shown in FIG. 9 may be amplifiers and Schmitttrigger circuits for the amplification and wave-shaping of the pulsesfrom the detectors.

The "column sync" signals shown in the waveform diagrams of FIG. 8 arethe ones that are counted by the margin counter. These signals aredeveloped in the following manner. A column sync counter 212 isprovided. It includes two J-K type flip-flops 300 and 302. Flip-flop 302receives the signal from the C sensor on its clock input, and bothflip-flops 300 and 302 receive the B sensor signal on their "clear"leads.

Referring now to FIG. 7 of the drawings, the disc 54 rotatescounter-clockwise. The sensors A, B and C produce signals when atransparent portion of the disc 54 is between the LED and thephoto-transistor, allowing light to reach the latter. Therefore,whenever a transparent area of the disc 54 is opposite the B sensor, the"clear" input leads of the flip-flops 302 and 300 are driven low so asto reset the column sync counter 212. When the wide mark 168 (2.5 timesas wide as any of the marks 166) passes through the sensor B, thistemporarily removes the "clear" signal from the flip-flops 300 and 302,and enables them to count pulses received from the sensor C, which nowsenses the narrow marks 166. Although it might seem that the thin marks166 are ending at the time the wide mark 168 first is detected by sensorB, this is not so because the wide mark 168 is 64.1° from the forwardend of the train of marks 166, whereas sensor B nominally is only 60°from sensor A. Therefore, sensor C then is 220° clockwise away fromsensor B, and the end of the thin marks 166 is 224.1° away, and therestill are several marks 166 left to pass through sensor C. Thus, thecounter counts up to two before the wide pulse 168 ends and the counteragain is cleared. This produces an output pulse on Q of flip-flop 300.This pulse is the "column sync" signal shown in FIG. 8 and appearing online 248 of FIG. 9.

After the wide pulse passes sensor B, but before the thin lines reachsensor B, the counter remains cleared, and no "column sync" signal isproduced. After the thin lines 166 reach sensor B, and also later whenboth sensors B and C sense the thin lines, the counter 212 is reset oncefor every transparent space between thin lines, and cannot, therefore,count to two and cannot produce a "column sync" signal. As a result, the"column sync" signal is produced only once per revolution of the disc54, at the time when the wide mark 168 passes through sensor B.

As it has been noted above, the "column sync" signals are delivered overline 248 to the margin counter 246 which counts two of the signals. Thecounter 246 then delivers an output signal over line 250 to start theprinting operation.

STARTING PRINTING

Referring to the lower central portion of FIG. 9, the signal on line 250of the margin counter 246 is delivered to the clock input of anotherD-type flip-flop 251 which changes state and develops a signal on its Qoutput line. This signal is supplied over line 254 to the margin counterto inhibit it, and also is supplied over line 252 as a "start" signal toa printenabling flip-flop 254.

Flip-flop 254 is a D-type flip-flop which is clocked by signals appliedto its clock lead 253 from an AND gate 290 which is in the right-centralportion of FIG. 9. AND gate 290 receives an enabling input on its lowerlead, and is enabled by pulses from the A sensor received over line 298.This, in effect, sends the pulses from the A sensor through to the clockinput of the flip-flop 254. Thus, the first of the pulses developed bythe thin lines 166 on the code disc in the A sensor, together with the"start" signal on line 252, causes a change of state in the flip-flop254. The subsequent clock pulses from the A sensor also time the lateroperation of the flip-flop 254. This operation of flip-flop 254 changesthe state of the Q output line 256 and the Q output line 274.Simultaneously, the "high" signal on line 256 is applied to one input ofanother NAND gate 260 whose other input also is high due to beingconnected to the Q output of another D type flip-flop 258, which is"cleared" at this time.

ROW COUNTER

The output of gate 260 enables the row counter 262 whose function is tocount the rows of dots being printed, as well as the spaces in-betweenlines of characters; to address the ROM code converter 202 over addresslines 264, 266 and 268 and cause it to deliver its information throughAND gates 272 and amplifiers 314 to the brushes 106 and then to thestyli 68. Of course, none of the AND gates 272 will produce a properoutput signal unless both of its inputs are in the same state.

One of the inputs of each of the gates 272 is connected to the output ofa three-input positive NAND gate 270. The output of gate 270 enableseach of the AND gates 272 when the signal on each of input leads (274and 276) is in the proper state. The signal on line 274 is in the properstate whenever flip-flop 254 is "set" in order to enable printing. Lead276 is connected to one output terminal 284 of a multiplexer circuit 282(in the lower right hand portion of FIG. 9) which, as it will beexplained further below, always receives the pulses produced by the thinlines 166 in the sensors A, B and C. Thus, the gate 270 is enabledrepeatedly by the timing pulses produced by the thin lines 166, but onlyduring the short duration of those pulses.

The timing pulses also are delivered from line 284 to the row counter262 over a line 263. The row counter counts the time pulses and thussteps through its addressing routine and counts the number of rows beingprinted. Since there are seven dots vertically in each character, therow counter steps through seven pulses, repeatedly changing thecombination of outputs on lines 264, 266 and 268 to sequentially addressthe ROM code converter 202.

On the eighth count line 271 of the row counter goes "high". Thisinhibits the gate 270 and sends an enabling signal over the "clear" line277 to enable flip-flop 258. Flip-flop 258 does not actually change itsstate at this time because it is a "D" type device which requires aclock pulse on the clock input to enable it to change. The signal online 271 also is sent to the line counter 278 to advance it by onecount.

LINE SPACING SELECTION

The clock output line 257 of the flip-flop 258 actually can be connectedto either line 264 or 268 in order to select the spacing between linesof characters. Line 264 is energized when the counter 262 counts up totwo, and line 268 is energized when the counter 262 counts to five.

Assuming a line spacing of two has been selected by connecting line 257to line 264, on the ninth count by the row counter 262, line 264 goeshigh, and this sets flip-flop 258. If a line spacing of five isselected, the same action takes place at a count of twelve instead ofnine.

READING THE NEXT CHARACTER

When the flip-flop 258 is set, its Q output goes high and delivers asignal to activate a one-shot multivbrator 261 in the memory controlcircuit 206 in the upper left portion of FIG. 9. The one-shotmulti-vibrator produces a pulse which is delivered through gates 219,220 and 222 to read/write line 224 to read out from memory 200 theinformation for another character. It should be noted that theinformation for the first character already appeared on the output leadsof the memory 200 because that was the first information that was storedin the memory 200.

The setting of flip-flop 258 causes its Q output to go low, which causesthe output of gate 260 to go high and reset all of the outputs of therow counter of 262 to zero. The resulting low signal on lines 271 and277 resets flip-flop 258 and again enables gate 270 to permit the nextcharacter to be printed.

The row counter 262 now starts anew to count timing pulses received overthe line 263, and the printing of the next character in the column isstarted. The next character is printed in the same manner as the firstcharacter, and the process is repeated until a character has beenprinted in each of the twelve or twenty-four lines in which charactersare to be printed. Thus one column of characters has been completed.

LINE COUNTER

The signal on output lead 271 from the row counter 262 also is deliveredto a line counter 278 which counts the number of lines which have beenprinted in any pass of a print head over the record strip. Two differentconnections are provided to the line counter 278, one enabling theinternal circuitry to count up to twelve lines, the other enabling it tocount up to twenty-four lines, at the option of the user.

Assuming that twelve lines are to be printed, after the twelfthcharacter has been printed by a particular print head, the line counter278 delivers an output signal over line 280 to an AND gate 282 whichalso receives an input from flip-flop 236 over line 240 so that theflip-flop 254 now is cleared. This disables the printer until it is timeto start the next vertical column of characters when the next print headis in position to start printing.

DOT TIMING

The dot timing circuit 210 includes, in addition to the multiplexer 282and the column sync counter 212, a data select counter 214 and adivide-by-117 counter 288.

The multiplexer 282 connects different input signals to the output leads284 and 286 depending upon the state of the input lines 291 and 292. Thefollowing table describes the operation of the multiplexer:

    ______________________________________                                        TRUTH TABLE FOR MULTIPLEXER 282                                               291     292    284    286   Function Permitted                                ______________________________________                                        (1)  0      0      A    B     Print Column A                                  (2)  1      0      B    C     Print Column B                                  (3)  0      1      C    --    Print Column C                                                                Column Sync Signal Resets                                                     to Condition (1)                                ______________________________________                                    

The data select counter 214 includes a pair of J-K type flip-flops 304and 306. When the first pulse from the divide-by-117 counter 288 changesthe state of flip-flop 304, this changes the data at the output lines284 and 286 in accordance with the above table. When the next pulse isreceived from the circuit 288, the state of the second flip-flop 306 ischanged, and data on lines 284 and 286 change again in accordance withthe table. In this way, first the A signals then the B signals and thenthe C signals are delivered to the circuit to control the printing.

Referring now to FIG. 8, the "column sync" signal occurs at time t_(o),and the sensor timing signals start shortly thereafter, at time t₁.Referring now particularly to the "B" sensor waveform in FIG. 8, it canbe seen that the B sensor starts producing timing pulses at time t₂.Referring again to FIG. 9, the pulses from sensor B are delivered overoutput lead 286 of the multiplexer to the divide-by-117 counter 288.Printing by the "A" stylus head ends at t₃ (FIG. 8) when the linecounter clears the print-enable flip-flop 254. When the counter 288 hascounted 117 pulses (one-third of the 351 pulses produced by the thinmarks 166 on the disc) the counter 288 produces an output signal whichis delivered to one input of an AND gate 294 whose other input isconnected to the Q line of the flip-flop 300. Thus, AND gate 294 isenabled and sends a signal over line 296 to clear the line counter 278.This removes the output from the line counter on line 280 and therebydisables AND gate 282 and causes the print-enable flip-flop 254 tochange state and start the "B" print head to printing another column ofcharacters. This occurs at time t₄, a short time after t₃.

From time t₄ to t₆, the "B" stylus head prints characters. At t₆, theline counter again operates to stop the printing. In the meantime,timing pulses from the "C" sensor have been delivered to the counter 288since t₅. When counter 288 again produces an output after having counted117 pulses from sensor C, the third stylus head is enabled to startprinting at t₇, until the line counter stops the printing at t₈. Thenthe column sync pulse occurs again at t_(o) and the printing process isrepeated again for another revolution of the rotor 28. This is repeatedover and over again until all of the information in the memory 200 hasbeen read out and printed.

During the readout of information from the memory 200, the shiftregister 232 shifts the same number of times as each of the shiftregisters in the memory. When register 232 is full, a circuit (notshown) is provided which delivers a pulse over line 234 to returnflip-flop 236 to its initial state, de-energize the motor drive circuit208, and stop the motor. This same circuit also resets any of the shiftregisters or flip-flops which have not already been reset, in order toprepare the circuit for the next printing job.

REPEAT PRINTING

If it is desired to repeat the same printing job to make duplicatecopies of the text, this can be accomplished simply as follows. Prior toloading the memory, the "R strobe" input to the shift register 232 andthe "R" input to the shift registers in the memory 200 are connectedtogether and to a low signal source. The shift registers are of a typein which this causes the data to be re-circulated and re-stored in theshift registers of the memory 200 instead of being destructively readout. The same is true for the shift register 232. Thus, in this mode ofoperation, the printer automatically will print the same text matteragain and again, as many times as desired.

AUTOMATIC BLACKNESS CONTROL CIRCUIT

In accordance with another feature of the invention an automaticblackness control circuit 215 is provided. This circuit comprises aone-shot multi-vibrator tachometer 308 whose output is delivered to anintegrator circuit 310 whose output is amplified by a linear amplifier312. The output of the amplifier 312 is delivered to the inputs of theamplifiers 314 in order to increase or decrease the voltage applied tothe styli in accordance with the speed of the rotor.

The pulses delivered over line 284 have a frequency which is directlyproportional to the rotor speed, since these are the fine pulsesproduced successively by the lines 166 in sensors A, B and C. The pulsesat the output of the tachometer 308 have constant widths, since theirwidths are determined only by the characteristics of the multivibrator.However, since the time periods between the pulses varies with the speedof the rotor, the output of the integrator 310 varies in directproportion to the rotor speed. This increases or decreases the output ofthe amplifier 312, and the amplifiers 314. As an example, in a preferredembodiment of the invention which has been built and successfullytested, the voltage applied to the styli was 50 at a printing speed of[from] 500 characters per second. At 3,000 characters per second and thesame number of lines and line spacing, the stylus voltage was 70 volts.

By means of the automatic blackness control circuit, the blackness andreadability of the printed characters is maintained at a relativelyconstant level despite such wide variations in speed of the rotor. As ademonstration example, highly satisfactory printing has been producedwhen the rotor is merely rotated by hand at a very low speed, as well asat speeds of up to 3,000 characters per second.

It should be understood that the speed of 3,000 characters per second isnot believed to be the upper limit of speed for this device. This speedwill vary with the number of lines of characters being printed, etc.However, it is a significant advantage of the invention that a speed ofup to 3,000 characters per second has been achieved in a relatively lowcost, simple and compact machine.

USES AND VARIATIONS

It is envisioned that the present invention will have wide utility inprinting alphanumeric characters. For example, it is believed that thisinvention will be especially useful in producing "hard copy" from acathode ray tube or television screen at a computer terminal orelsewhere. The "page" of data appearing at any one time on the cathoderay tube screen can be printed out as a unit rather easily. The printerof the present invention is so small (e.g. 4 inches by 4 inches by 8inches or smaller) that it can be fitted into the same module with manycathode ray tube display screens.

The printer can be used advantageously in many applications where smallsize is important. For example, the printer is useful in aircraft,spacecraft, police, fire and other emergency vehicles.

It is believed that the printer of the present invention will makeexcellent low-cost, reliable stock quotation printer, especially whenoperated in the mode in which the printing is composed in a single line.

As one alternative embodiment of the invention, the logic circuitry of acomputer terminal can be used to replace some of the control circuitryshown in FIG. 9. Alternatively, the printer control signals can beprovided by specially programming a general purpose computer.

Although it is preferred that the electrical discharge process be usedin the present invention, the three print heads on the rotor also canhave other constructions. One is the use of a group of push-rods insteadof styli for each of the heads. In such an embodiment, each of the pushrods is actuated by an electro-magnet to strike an inked ribbon or thelike in order to form characters in dot matrix form on ordinary paper.Devices forming dots from ink similarly can be used to form charactersfrom dots on ordinary paper.

The number of print heads on the rotor can be varied, as can the numberof styli in each head. However, the use of three print heads, with eachprinting one column of characters per pass, has been found to havedecided advantages. It will be noted in FIG. 3 that there is a slightvariation from left to right of the starting point of the top and bottomlines of print. This is because, as the rotor is rotating, the recordingpaper is continuously moving, which means that the positon at which thelast line starts will be displaced longitudinally by a small amount fromthe place where the first line starts. It has been found,advantageously, that this slight amount of skew usually is notobjectionable in data printers, and need not be compensated for.However, if it becomes objectionable in a particular use of the printer,the skew can be compensated in the manner shown in FIG. 13.

FIG. 13 is a schematic plan view of a printer like that shown in theprevious figure of the drawings, except that the direction of paper feedis at an angle θ of 2 degrees and 4 minutes from the longitudinal axisof the printer, an angle which is sufficient to compensate for the skewproduced by the printer. Of course, if variations in the number of headsand/or stylus wires are made, the compensation angle θ can be varied asnecessary.

Although a mechanical system has been described for alignment of theprinting by the three heads, one in which the adjustment is made byturning the cam wheels 158 and 160, the same adjustment can be made bypurely electronic means. In this modification, the same function can beperformed by the adjustment of counters which time the start of printingby each of the heads so as to cause the printing by that head to lead orlag the printing of the others by a certain amount. With presenttechnology, however, it is believed that the mechanical adjustmentdescribed above gives good precision at a lower cost than it wouldrequire to obtain the same precision by electronic means.

MATERIALS AND SPECIFICATIONS

Following are specifications for some of the materials and components ofa printer which has been constructed and successfully tested inaccordance with the present invention.

Suitable recording paper is readily available. Suitable papers, coatedwith a black opaque material and then coated with either aluminum orzinc oxide, have been obtained from Fitchberg C.P.I,, Scranton, Pa., andfrom AtlanTol Industries. The preferred paper has a total thickness of0.002 inch. The aluminum-coated paper is desirable because it oftenrequires lower stylus voltages in order to vaporize the aluminum coatingto expose the black material underneath.

Styli which have been used successfully have a diameter of 0.007 inch,and are spaced approximately 0.016 inch from one another, center-line tocenter-line. The desired spacing of the dots on the paper isapproximately 0.016 inch, both in the horizontal and in the verticaldirection. It should be noted, however, that sometimes there is a smallvertical extension of the dots due to the rotation of the rotor. Whenprinting characters, this sometimes improves the printing in that ittends to fuse the dots together into solid vertical lines.

The material of the styli is thoriated tungsten. The most desired rangeof angles between the styli and the platen is 60° to 70° (see FIG. 6).

It is preferred that as much of the body of the printer as possible bemolded out of plastic in order to achieve low cost and light weight.Thus, although the main drive shaft 48 is made of metal, the housing 24and many other parts are molded out of reinforced plastic.

The platen 26 preferably is molded out of glass-filled "Lexan"polycarbonate plastic material, or out of glass-filled nylon. Suchmaterials are preferred for the platen because it must be electricallynon-conductive, and yet must have good wear characteristics.

A.D.C. motor which has been found to be suitable for driving the printeris manufactured by Barber-Coleman Co., part number FYOM-63200-51. It hasa diameter of 1.26 inches and a length of 1.95 inches. Its operatingvoltage is 12 volts D.C. and has a torque output of 1 ounce-inch at 4400R.P.M. and 1.3 Amperes.

The optical sensors 146 used to sense the marks on the timing disc 54are made by Optron Corporation. The sensor is called an "opticalswitch", part number OBP800. Also suitable is a similar device made bySpectronic, Part No. PNSPX 1872-s. The sensor has been modified simplyby adding a mask as described above in the specification.

The code used to encode characters is the well-known code called ASCII.This is advantageous since code converters for use with such a code arereadily available.

In the electrical control circuit of FIG. 9, certain of the componentswill be identified specifically below. The components are readilyavailable from several different sources unless it is indicatedotherwise.

    ______________________________________                                        COMPONENT        IDENTIFICATION                                               ______________________________________                                        Rom Code Converter 202                                                                         2512 "Character Generator"                                                    Manufactured by Signetics Corp                                                operates on ASCII II code                                    Shift registers in Memory 200                                                                  Integrated circuit shift                                     and Shift Register 232                                                                         register 2529, with data                                                      recirculation feature.                                       "Flip-Flops" 236, 251, 254, 258,                                                               Integrated circuit D                                                          type (flip-flops) bi-stable                                                   multivibrators.                                              "Flip-Flops" 300, 302, 304 and                                                                 74LS73 J-K type integrated                                   306              circuit (flip-flops) bi-stable                                                multivibrators.                                              Multiplexer 282  Integrated circuit multiplexer                                                type 74153.                                                  Row counter 262  Integrated circuit 4 bit-                                                     counter connected as a divide-                                                by-16 circuit                                                Margin space counter 246                                                                       74LS90 integrated circuit                                                     counter connected as a divide-                                                by-2 circuit.                                                Line counter 278 74LS190 integrated circuit                                                    counter with 74LS74 flip-flop                                                 connected at the input as a                                                   divide -by-2 circuit.                                        Gate 270         Number 7427 integrated circuit                                                plus NOR gate.                                               Integrator 310   A741 operational differential                                                 amplifier with capacity feed-                                                 back.                                                        One-shot tachometer 308                                                                        An integrated circuit 74LS121                                                 one-shot mulivibrator                                        AND gates 272    Integrated circuit No7403 NAND                                                gates                                                        Gates 222, 282, 294, 290                                                                       Integrated circuit 74LS08 AND                                                 gates                                                        Counter 288      Two 74LS193 integrated circuit                                                counters connected as a divide-                                               by 117 circuit                                               OR Gates 218, 219 and 220                                                                      74LS02 integrated circuit NOR                                                 gates                                                        ______________________________________                                    

The above description of the invention is intended to be illustrativeand not limiting. Various changes or modifications in the embodimentsdescribed may occur to those skilled in the art and these can be madewithout departing from the spirit or scope of the invention.

I claim:
 1. In a rotary electrical discharge printer having a rotor, aplurality of styli projecting from said rotor, a voltage supplyconnected at one terminal to said styli, means for moving electricaldischarge-sensitive sheet recording material across said rotor incontact with said styli, an electrical contact brush for said materialcomprising an electrically conductive helical spring positioned on thesame side of said material as said styli and extending transversely ofthe direction of recording material movement to contact and pressagainst said material, and means for connecting said spring to thereturn terminal of said voltage supply.
 2. A device as in claim 1including guide means for assisting in the curving of said sheetmaterial, including a curved rod passing through the center of saidspring, and also including means for mounting said rod and spring in aposition where said spring urges said sheet material against said guidemeans.
 3. A device as in claim 1 in which said sheet material is a paperstrip, and including guide means for curving said paper to conform tothe shape of said rotor, said spring being bowed into an arcuate shapeand fitted into the concave area of the curved paper stirp.